1. Field of the Invention
This invention relates to an impact type printer using, for example, a daisy wheel or the like to effect printing.
2. Related Background Art
As one of the main types of electronic typewriters and printers, there is the so-called impact type printer which strike a type member such as a daisy wheel or the like by a printing hammer to thereby accomplish printing. In such an impact printer, there has been the problem that when impact is effected by the printing hammer, the time for which a solenoid is energized is constant and therefore the output of the hammer is also constant and between the initial stage and the stage after use, the type portion of the type band is worn to deteriorate the quality of print. To solve such a problem, it is known to select time tables in order to obtain a stable output of the printing hammer even if the printer is used for a long period of time, as is known from Japanese Patent Application Laid-open No. 58-58278. That is, this is a system in which the operating speed of the hammer in the printing direction thereof is detected by a detecting coil and one of two or more sets of energization time tables of the hammer is selected in conformity with the result of the detection of the detecting coil to control the output of the hammer.
Also, the impact type printer system has the advantage that a high quality of print is obtained, while it suffers from the disadvantage that the noise during printing is great. One of the causes of this noise is the impact sound produced when the printing hammer is returned to the standby position after printing and strikes against a stopper, and as a method of decreasing such sound, it is known from U.S. Pat. No. 4,744,684, etc. to effect the second power supply to the solenoid before the printing hammer strikes the stopper, thereby imparting a damping force to the hammer.
The applicant improved on such a prior-art system and proposed, in Japanese Patent Application No. 61-66008 (U.S. application Ser. No. 029,686), to detect the return speed of the hammer, and brake the recording hammer by a damping force conforming to result of the detection. Further, the applicant proposed, in Japanese Patent Application No. 61-216051 and Japanese Patent Application No. 61-224906 (U.S. application Ser. No. 094,894), to detect the return speed of the hammer and determine the timing for braking the recording hammer in conformity with the result of the detection.
In such system, the impact sound of the hammer is very effectively decreased if the printer is used within a certain temperature range.
However, when the environmental temperature becomes low and the platen becomes very hard, the repulsion force of the platen increases remarkably and the return speed of the hammer becomes very high, and this has led to the undesirable possibility that there is insufficient time to effect the second power supply to the solenoid before the hammer strikes the stopper and thus, the hammer cannot be braked.
That is, when the environmental temperature becomes low, the return speed of the hammer becomes very high and the timing for braking the hammer is too late with the result that the impact sound of the hammer becomes vehiment. Also, if the second power supply is effected when the hammer strikes against the stopper and is bounded thereby, there has been the undesirable possibility that they are compounded to result in multiplex printing.